soc: ti: k3-ringacc: Allow the driver to be built as module

The ring accelerator driver can be built as module since all depending
functions are exported.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@gmail.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Tested-by: Nicolas Frayer <nfrayer@baylibre.com>
Reviewed-by: Nicolas Frayer <nfrayer@baylibre.com>
Link: https://lore.kernel.org/r/20221029075356.7296-1-peter.ujfalusi@gmail.com